Series-Connected LED Backlight Control Circuit
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Solution Overview
Problem
Conventional LED backlight control systems for displays suffer from color perception changes during dimming, leading to suboptimal contrast ratios and inefficiencies in power dissipation, particularly due to the need for precise current control and the complexity of existing circuit designs.
Innovation Solution
A circuit for controlling a series-connected LED backlight with floating switches, utilizing capacitive or inductive coupling for control signal transmission, and incorporating local power supplies and demodulation means to achieve high-speed, precise, and efficient illumination modulation, allowing for constant current delivery and minimizing power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional LED dimming control is used by varying current, then light intensity is adjusted, but color perception changes which is undesirable
Solution Approach 1:
The patent employs pulse-width modulation (PWM) to control LED backlight intensity. Instead of varying current continuously, the system switches LEDs on and off in periodic pulses with variable duty cycles. This periodic switching maintains constant LED forward current when on, preventing color shift while achieving dimming through temporal averaging of light output.
Solution Approach 2:
The patent maintains continuous LED operation at constant current by using high-frequency PWM switching. The LEDs remain continuously connected to the constant current source, and the perceived dimming effect is achieved through rapid on-off cycling that is imperceptible to the human eye, thus maintaining color stability while controlling intensity.
2Illumination intensity
If LED backlight intensity is controlled for improving contrast ratio, then brightness is adjusted, but circuit complexity increases due to precise current control requirements
Solution Approach 1:
The patent combines multiple functions into a single integrated control architecture. The constant current source, PWM generation, and LED driver are merged into a unified circuit system. The control circuit generates PWM signals that directly modulate the constant current source, eliminating the need for separate dimming control circuits and reducing overall system complexity.
Solution Approach 2:
The control circuit is designed to self-regulate the LED backlight intensity through automatic PWM duty cycle adjustment. The system monitors its own operation and adjusts the duty cycle to maintain the desired brightness level without requiring complex external control mechanisms, thereby simplifying the overall control architecture.
3Illumination intensity
If LEDs are switched in pulsed manner for intensity control, then perceived light intensity is adjusted, but power dissipation efficiency decreases
Solution Approach 1:
The patent uses high-frequency PWM switching where LEDs are turned on during active periods and off during brief intervals. The switching frequency is sufficiently high that the LEDs remain warm during off periods, minimizing thermal cycling losses. The duty cycle is optimized to maintain average brightness while minimizing switching losses and maximizing energy utilization efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables globally or locally controlled LED backlight intensity with high precision and efficiency, reducing power dissipation and maintaining consistent color perception, while simplifying the control circuitry and reducing heat generation.
Implementation Method 1
The coupling means comprise capacitive or inductive coupling, e.g. via capacitors or transformers
Implementation Method 2
The coupling means comprise capacitive or inductive coupling, e.g. via capacitors or transformers
Data Source
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AI summary
A circuit for controlling illumination means in a display includes illumination means arranged in a series-connection that are supplied with an essentially constant current. For individually controlling the illumination means, switches are provided for bypassing individual illumination means, maintaining the essentially constant current in the series-connection. The switches are floating with respect to a ground potential. A coupling means is thus provided for proper control of the switches. In a development of the invention a floating local power supply is provided with each illumination means and switch for operating the switch. The local power supply is, in one embodiment, powered by the control signal that is used for controlling the bypass switch. In another embodiment provision is made for supplying power to the floating local power supply. A driving method according to the embodiments of the circuit is also described.